This invention relates generally to tennis rackets or the like and, more specifically, to a racket formed from reinforced plastic materials.
Strung rackets for use in tennis and similar games have long been made from solid wood and strung with gut or nylon strings. Manufacture of high quality rackets is a complex process. Despite great care in manufacture, the playing characteristics of wood rackets vary greatly due to natural variations in the wood used and manufacturing process variables.
Playing characteristics of wood rackets also vary with changes in temperature and humidity and with age of the racket, which changes may also cause the head to warp due to varying string tension.
Recently, steel and aluminum rackets have been developed in order to obtain greater uniformity. However, it has been found that these metal rackets do not provide the same playing qualities as wood rackets, since sufficient stiffness cannot be provided without excessive weight. Also, metal rackets frequently have short useful lives, due to cracking apparently caused by metal fatigue or stress concentrations.
Rackets are also being manufactured from fiberglass reinforced plastics. These rackets, however, generally are overly flexible and do not provide the desired stiffness for equivalent weight. Also, they lack uniformity and are expensive due to the number of manual manufacturing steps.
No matter which material has been used, there have always been problems in providing sufficient strength in the racket head to resist stresses during stringing of the racket. As stringing progresses, severe stress concentrations result in portions not yet supported by strings. As stringing continues, the locations of stress concentrations shift. The racket frame may severely warp or break due to these stresses if the frame lacks the strength and stiffness to resist the stresses induced by the very taut strings. Generally, attempts to strengthen the frame by increasing its cross-section area have not been successful due to the resulting weight increase and balance shift to the head.
Thus, there is a continuing need for rackets of improved strength, stiffness and playing characteristics.